1. Technical Field
The present invention relates to a resonator element, a resonator, an electronic device, and an electronic apparatus.
2. Related Art
Electronic devices such as crystal oscillators mounted on electronic apparatuses include a resonator such as a crystal resonator. A resonator having a tuning-fork resonator element including two resonating arms extending to be parallel to each other is known (for example, JP-A-4-348606).
For example, in the crystal resonator described in JP-A-4-348606, two pairs of electrodes are disposed on a pair of surfaces facing each other in the width direction of each resonating arm having a rectangular section in the width direction. Among two pairs of electrodes, by applying voltages with inversed polarities to one pair of electrodes facing each other and the other pair of electrodes facing each other, each resonating arm can be made to vibrate in a torsional mode.
By using this torsional vibration, it is possible to reduce the variation in frequency due to a temperature variation, compared with a resonator using flexing vibration.
However, in the crystal resonator described in JP-A-4-348606, since the section in the width direction of each resonating arm is rectangular as described above, the torsional rigidity of each resonating arm is relatively high and the driving frequency cannot be satisfactorily lowered. When the resonating arm is narrowed to lower the torsional rigidity, the forming area of the electrodes is reduced, thereby not efficiently exciting the torsional vibration.